Lymphocytes "home" from the blood into lymph nodes as part of the process of lymphocyte recirculation. This homing process has multiple steps consisting of a sequence of adhesive and signaling interactions. The initial event is the rolling of the lymphocyte on high endothelial venules (HEVs) within the lymph node. This is followed by arrest and transmigration of lymphocytes into the lymph node. The rolling step is mediated by L-selectin, which recognizes a set of carbohydrate-based ligands on HEVs. The predominant ligands are sialomucins modified by sulfated sLex determinants and are known as PNAd. Considerable progress has been made towards the molecular characterization of these ligands and the identification of the sulfotransferases involved in their synthesis. Importantly, non-PNAd ligands for L-selectin exist on HEVs, other vascular endothelium and subpopulations of leukocytes. In addition, unidentified ligands for E-and P-selectin exist on leukocytes. Endoglycan is a close relative of CD34 and podocalyxin, but unlike them it is modified by chondroitin sulfate. Although not a member of PNAd, it is present in on a subset of human tonsilar HEVs. It is also highly expressed on activated B-cells. Recombinant endoglycan can function as a selectin ligand through the use of 2 tyrosine sulfate modifications and an sLex determinant on a neighboring O-glycan. A major aim of the proposed research is to evaluate the selectin ligand functions of endoglycan on vascular endothelium and leukocyte subpopulations, in particular activated B-cells. The possible role of endoglycan as a proteoglycan involved in chemokine presentation (e.g. CCL21) by HEVs will also be explored. In the final step of the homing, the lymphocyte becomes motile and migrates across the HEVs to gain entry into the lymph node. Autotaxin, a known motility stimulating factor for certain cancer cells, is highly expressed in HEVs of lymph nodes. This ectoenzyme catalyzes the production of the phospholipid mediator, LPA. Since LPA can promote the motility of lymphocytes, autotaxin may have a key role in stimulating the migration of arrested lymphocytes into lymph nodes. Understanding the basic process of lymphocyte homing will ultimately aid our understanding of leukocyte trafficking into inflammatory site, since many of the same mechanisms appear to be utilized. As the molecular machinery of normal lymphocyte homing is elucidated, new targets for anti-inflammatory therapeutics are likely to emerge.